Conventional chemical based propulsion systems commonly deployed in rockets rely on an oxidizer, such as oxygen, to generate a chemical reaction in order to create thrust. Nuclear thermal propulsion (NTP) systems have the potential to deliver thrust values that far exceed chemical based fuels. Typically, this is done by heating a propellant, typically low molecular weight hydrogen, to over 2,600° Kelvin by harnessing thermal energy from a nuclear reactor.
NTP is an appealing technology with prospects for becoming the propulsion system of choice for human missions beyond low earth orbit. Numerous mission architectures call NTP the preferred approach for a 2030s human Mars mission for its ability to produce significant amounts of thrust while operating at a high specific impulse.
The design of NTP systems dates back to the Nuclear Engine for Rocket Vehicle Applications (NERVA) work done by NASA. The NERVA design typically consists of a small nuclear fission reactor, turbopump assembly (TPA), nozzle, radiation shield, assorted propellant lines, pressure vessel, and support hardware. Thermal energy gained by the propellant during an expansion cycle is used to power the rocket.
In conventional NTP designs, control drums are used to adjust reactor reactivity. Unfortunately, reactivity control of NTP reactors through the use of the control drums can be problematic in terms of operating requirements and effect on the performance of the propulsion system.